1. Field of the Invention
This invention relates to a tube core and a pair of holders for a stencil sheet roll which is mounted in a stencil printing machine when used.
2. Detailed Description of the Prior Art
As shown in FIG. 5, the stencil sheet roll R is conventionally produced by winding a length of stencil sheet 12 around,a cylindrical tube core 11. The tube core 11 is generally made of used cardboard and shaped like a cylinder. This tube core 11 may also be called a cardboard spool.
To mount the stencil sheet roll R in a stencil printing machine, a pair of holders H are required which are installed in both end openings 13, 14 of the tube core 11. Each holder H is formed by a disk-shaped guide plate 21 which extends along the end surface of the roll R to guide an edge of the stencil sheet 12 drawn from the roll R, and a cylindrical projection 22 like a stub concentrically projecting from the guide plate 21. The holder H can be installed in the roll R by inserting and fitting the projection 22 into each of the end openings 13, 14 of the tube core 11 in a plug-in manner. An external diameter of the projection 22 is designed to be almost equal to an internal diameter of each of the end openings 13, 14 of the tube core 11, and therefore the projection 22 can be inserted and fitted into each end opening 13, 14 of the tube core 11 as it is.
In order to cope with various applications, it has recently been required for stencil printing machines to be varied in type with respect to the size ranging from a large machine to a small machine, or with respect to the resolution ranging from a low-resolution machine to a high-resolution machine. Accordingly, the stencil sheet is sometimes required to be different in its properties according to the type of the machine. Therefore, it is necessary to prevent a stencil sheet from being erroneously mounted in an irrelevant machine.
To eliminate the erroneous mounting, various preventive methods have been suggested. For example, it is proposed, in Japanese Utility Model Laid-Open No. 83769/1992, that notches or projections are formed in or on the end surface of the tube core, which are different in shapes according to types of the stencil sheet. Alternatively, the tube core is subjected to a specific treatment for discriminating the types of the stencil sheet. These proposed methods, however, have inconveniences such that processing of the tube core requires preciseness, or manufacturing cost of the tube core unfavorably becomes expensive.
It is therefore an object of the present invention to provide a tube core for a stencil sheet roll, and holders adapted to fit in the tube core, which are simple in construction and low in cost, and capable of preventing the roll from being erroneously mounted in an irrelevant machine without fail.
To attain the object, the present invention provides a tube core for a stencil sheet roll, having two end openings adapted to receive a holder that has a guide plate for guiding an edge of the stencil sheet and a projection projecting from the guide plate for fitting in the opening, in which said openings are different in inner dimension from each other, whereby they receive holders different in dimension of said projection.
The tube core is generally comprised of a cylindrical main body, and the openings thereof can be formed at both ends of the tube core, e.g. by arranging circular openings different in internal diameter from each other, in a manner concentric with the main body. The circular openings different in internal diameter can be molded when the tube is integratedly formed of plastic. Alternatively, the main body may be formed, e.g. by a cylindrical first tube, and one opening of the main body may be one of the end openings of the first tube, while the other opening may be defined by an end opening of a second tube which has been nested and secured in the first tube at a location neighboring to the other end opening of the first tube.
The second tube may be arranged such that an end thereof may be flush with the other end of the first tube. Alternatively, the second tube may be arranged at a location internally spaced a predetermined distance away from the end of the first tube such that a step portion is formed between the end of the first tube and the end of the second tube. In the latter case, the holder may have a shoulder portion formed thereon, which is shaped to be complementary with the step portion, whereby the shoulder portion is housed in the step portion in the tube core at the time of installation of the holder. As a result, combination of the external diameter of the projection of the holder and the dimension of the step portion makes it possible to differentiate varieties of stencil sheet rolls.
Thus, according to another aspect of the invention, there is provided a holder adapted to fit in a tube core of a stencil sheet roll, said tube core comprising a first tube and a second tube nested in the first tube to form an end opening having a step portion in the tube core, which comprises a guide plate for guiding an edge of the stencil sheet drawn from the roll, and a projection projecting from the guide plate and having a shoulder portion in a manner bordering on the guide plate and the projection so as to be housed in said step portion of the opening of the tube core. A spool for stencil sheet can be constituted by a pair of the present holders and the present tube core.